Why not make a low mobile charger that can fit under the car. Small metal plate with casters, 2-3 batteries on it in parallel, slide it under the car and leave in place, then whip it upstairs once a week and give it a charge. If you do this then watch for Captain Cock-up....
Make certain the terminals cannot contact the car at all.
Place a sign on the car to remind you when you are in a hurry.
Put a multi-meter in line to avoid flattening the pack and killing it.
Secure the batteries to the plate well to avoid risk of spill.
I used to do this for the race car many years ago as battery trucks were out of my budget in those days.
